In August, 2005, Hurricane Katrina decimated New Orleans. The human cost of this tragedy is well known. A paper published in the February 1, 2011 Journal of the American Veterinary Medical Association (JAVMA) summarizes what happened to many animals in the area during and after the event.

An unprecedented animal rescue operation followed the 2005 landfall of Hurricane Katrina in the Gulf Coast. An estimated 50,000 cats and dogs were left behind by fleeing owners, which was in addition to the unknown number of stray and feral animals in need of rescue.

Rescued dogs and cats found new homes throughout the US and beyond. In the fall of 2005 I began to see Hurricane Katrina rescues in my practice. And I noticed a startling trend: all of the dogs had heartworm.

Heartworm was quite uncommon in the Bay Area at that time. I hoped that environmental factors (our low humidity, low numbers of mosquitoes, and mild climate) would prevent the parasite from becoming entrenched. But the massive influx of heartworm-infested dogs led me to issue a warning to readers on October 20, 2005. Here’s an excerpt.

Heartworm disease is endemic (very common) along the Gulf Coast. The flooding caused by the storm created an ideal breeding ground for mosquitoes. Homeless pets stranded in the aftermath of Hurricane Katrina could not receive medications to prevent infestation with heartworm. Therefore, the pets (especially the dogs) rescued from the Gulf Coast are expected to have a very high rate of Heartworm disease.

In fact, every dog I have examined that was rescued from the Gulf Coast has tested positive for Heartworm disease. I have spoken to colleagues, and they have noticed similar results.

It is not certain that the importation of rescued animals will increase the incidence of Heartworm disease in any area. However, if you live in a region, such as the San Francisco Bay Area, where large numbers of rescued animals are now living, I strongly recommend you discuss Heartworm prevention for your pet with your veterinarian.

I can’t say that overall Bay Area heartworm prevalence has increased dramatically since 2005. However, the JAVMA paper studied the matter and concluded that Hurricane Katrina may have led to dispersal of heartworm and other vector-borne diseases to remote locales. The paper reports that 48.8% of a sample of Katrina dogs tested positive for heartworm.

Here are the authors’ conclusions:

Conclusions and Clinical RelevanceCats and dogs rescued from the disaster region had evidence of multiple infectious diseases. The dispersal of potentially infectious animals to other regions of North America where some infections were not typically found could have contributed to new geographic ranges for these organisms or to underdiagnosis in affected animals because of a low index of suspicion in regions with low disease prevalence.

And I stand by my original statement from the 2005 Vet Blog (back then it was called “Ask Dr. Barchas”) post:

Medications that prevent heartworm disease are reliable and convenient to administer, usually on a once monthly basis. Side effects are extremely uncommon, and the medications will help ensure that your pet is protected against this serious disease.